1. Field of the Invention
The present invention relates to a method for producing a plasma display panel (PDP).
2. Description of Related Art
PDPs are usually flat and have advantage in placement and power consumption over cathode-ray tube (CRT) displays. The general structure of PDPs will be explained taking for example an AC-driven PDP of a surface discharge type having three kinds of electrodes with reference to FIG. 5.
Referring to FIG. 5, a PDP 1 has such a structure that a glass substrate on the front side (front substrate) 11 is put together with a glass substrate on the rear side (rear substrate) 21 in an opposing relation. On the inside surface of the front substrate, a pair of sustain electrodes X and Y are disposed on each line L of a matrix for display. The sustain electrodes X and Y each include a transparent electrode 41 and a bus electrode 42. The sustain electrodes X and Y are covered with a dielectric layer 17 for AC-driving. On the surface of the dielectric layer 17, a protective film 18 is formed.
On the inside surface of the rear substrate, on the other hand, address electrodes A are disposed in stripes on a base layer 22. On the address electrodes, an insulating layer 24 is formed. On the insulating layer 24, barrier ribs 29 are formed to partition the address electrodes separately. In grooves between the barrier ribs, red, green and blue fluorescent layers 28R, 28G and 28B for color display are provided so as to cover the address electrode A. The barrier ribs 29 partition a discharge space 30 into sub-pixels in the direction of the line L and define the height of the discharge space 30 at a certain value, for example, 150 .mu.m. The discharge space 30 is filled with a gas for electric discharge for display. One pixel consists of three of the sub-pixels adjacent in the direction of the line.
For conducting display with this AC-driven PDP, a pixel is addressed for the display by electric discharge between one of the address electrodes and one of the sustain electrodes (e.g., Y electrode), and then, for maintaining the display, AC voltage is applied between the sustain electrodes X and Y to generate surface electric discharge for producing plasma for display via the dielectric 17.
The protective film 18 is provided to lower the firing potential at such electric discharge. Usually usable as the protective film 18 is MgO, which is a secondary-emission material which has high secondary emission efficiency and is hardly sputtered by the discharge gas for display.
CaO and SrO are also known as other materials having such secondary-emission characteristics.
However, most materials suitable for the protective film 18 easily react (having high deliquescence) with moisture or carbon oxides such as carbon dioxide in the air. Accordingly, when such materials are left in the air after they are formed into a film, the surface of the film is denaturalized. Therefore, when MgO is used as the protective film, for example, it is necessary to decompose the denaturalized layer formed on the surface of MgO by heating the panel to about 350.degree. C. at discharging impure gas inside the panel, after the assembly of the front substrate 11 and the rear substrate 21 into the panel with the discharge space 30 in between and with the periphery of the substrates sealed, and then to introduce the discharge gas for display.
In addition to MgO, CaO and SrO can also be used as the protective film. However, when CaO and SrO are used, higher temperatures than in the case of MgO are required for decoposing the denaturalized layer from the surface of the protective film. Therefore the protective film of these materials are not put into practice.
The formation of the protective film with MgO is known, for example, by Japanese Unexamined Patent Publication No. Hei 5(1993)-234519. In this reference, the protective film is formed as a &lt;111&gt; oriented film of MgO by vacuum evaporation in an atmosphere of oxygen or by ion assist vapor deposition using ion-beam irradiation.